text: One universal distinction between polymerization types is development of molecular weight by the different modes of propagation.  Addition polymers form high molecular weight chains rapidly, with much monomer remaining.  Since addition polymerization has rapidly growing chains and free monomer as its reactants, and condensation polymerization occurs in step-wise fashion between monomers, dimers, and other smaller growing chains, the effect of a polymer molecule's current size on a continuing reaction is profoundly different in these two cases.  This has important effects on the distribution of molecular weights, or polydispersity, in the finished polymer.